Heretofore, various types of swim fins have been provided to propel a swimmer underwater with increased speed. One type of swim fin angles the flipper part thereof downwardly relative to the longitudinal axis of the foot in order to take into consideration the posture and leg movements of the human body while swimming, and the direction of intended movement. It can be recognized that a swimmer has much less muscular power to apply during the upstroke portion of each cycle than during the downstroke. In view of such lesser power, the swim fin operates better when it includes normally open vents which are closed during each upstroke to increase the apparent area of the fin. This increase in area provides some decrease in the effort that is exerted by the swimmer to move forward through the water. However turbulent flow of water through such vents can increase the effort required on the downstroke considerably.
A related patent is U.S. Pat. No. 4,627,820 issued Dec. 9, 1986 to Penebre (U.S. Class 441/64) which discloses a swim fin having upper and lower rounded shells that surround a water flow area, and an outwardly extending web or flipper having about the same length as the shells. The flipper is attached centrally near the front ends of the shells, so that the shells together with the fin provide a considerably elongated construction. Check valves in the form of flaps or baffles operate alternately during the power and return kick strokes to increase the propulsion forces. However swim fins disclosed in this patent are quite long due to the fact that the valve assembly is located well to the rear of the fin itself, which is believed to reduce the overall efficiency as compared to the present invention. Moreover the swim fin disclosed in the '820 patent does not provide a structure in which the flexibility of the fin is increased in the toe region. The Lamont U.S. Pat. No. 4,775,343 issued Oct. 4, 1988 (U.S. Class 441/64) shows upper and lower slots providing a flexible fin, however this swim fin also is quite lengthy, which is believed to reduce efficiency.
A general object of the invention is to provide a new and improved swim fin assembly having a multi-level, relatively short construction which increases the efficiency and mobility with which a swimmer can move through the water.
Another object of this invention is to provide a swim fin of the type described which has upper and lower, relatively short fins, and check valve means associated with each fin for controlling the flow of water therepast in a manner that increases the overall efficiency of the fin assembly.